Explain the difference between trade-off and opportunity cost. I just need a short response. Thanks!

Which of the following is an example of the treatment technique for ocd called exposure and response prevention (erp)? a. callie has a hoarding compulsion. she becomes anxious whenever she has to throw something away; she even keeps stuff that she doesn't need and will never use. her therapist has arranged for callie's unnecessary belongings to be discarded of when she is away from home. b. carrie has an obsessive fear of contamination which has led to compulsive hand washing. her therapist is treating her by making her touch dirty laundry but not allowing her to wash her hands following for increasingly longer periods of time. c. kelly has religious obsessions. she feels that if she doesn't read biblical passages every hour of the day, she will do something evil. her therapist is treating her by having her attend religious services more frequently so that good thoughts will replace the bad ones. d. kerry has an obsessive fear of contamination which has led to compulsive hand washing rituals. her therapist is treating her by forcing her to wash her hands repeatedly, even when she doesn't feel anxious.